The present invention relates to a method and/or architecture for implementing a video field freeze filter generally and, more particularly, to generating a new frame from only one of two interlaced fields in an original frame.
Pictures presented in a Motion Picture Expert Group (MEPG) standard video format are frame-based or field-based. The frame-based video means that each frame contains two interlaced field images that are sampled at the same time. The field-based video means that each frame contains two interlaced field images that are sampled at different times. The field-based frames compliant with the National Television Systems Committee (NTSC) standards sample a new field every {fraction (1/60)}th of a second. Consequently, the two fields that comprise one frame are slightly shifted in time with respect to each other.
The time shift between the two fields of the one frame can cause distortion when both fields are repeated over and over to freeze the one frame. If an object appearing in the frame is moving relatively rapidly, then the object will appear in each of the two fields in different positions. When the two fields are repeated to freeze the frame, the object appears spatially distorted along the direction of motion and can even appear to flicker.
One approach that has been used to eliminate the spatial distortion is to display only one of the two fields when freezing the frame. A consequence of not displaying one of the two fields is that vertical resolution in the frame is reduced. Another approach that has been used to freeze the frame is aimed at eliminating the flickering and loss of intensity. Here, one of the two fields is replaced by a copy of the other field for display purposes. Since the displayed field and the copy of the displayed field have effectively the same sample time then there is no blurring of fast-moving objects. However, vertical resolution of the frame is still degraded. Furthermore, some objects, such as alphanumeric characters change noticeably in appearance as horizontal features double in height.
The present invention concerns a circuit for freezing a video frame having a first field interlaced with a second field. The circuit generally comprises a memory and a filter. The memory may be configured to present a plurality of coefficient signals that define (i) a first coefficient set for the first field and (ii) a second coefficient set for the second field. The filter may be configured to present a new frame in place of the video frame. it The new frame may be generated from (i) the first field and the first coefficient set in response to freezing on the first field and (ii) the second field and the second coefficient set in response to freezing on the second field.
The objects, features and advantages of the present is, invention include providing a method and/or architecture that may (i) freeze a 2:1 interlaced video frame based upon a single point in time, (ii) maintain an approximately normal intensity in the frozen frame, and/or (iii) maintain an approximately normal vertical resolution in the frozen frame.